1. Field of the Invention
This invention pertains generally to the field of vapor recovery devices associated with equipment for dispensing volatile liquids, such as gasoline pumps and dispensing nozzles.
2. Description of the Prior Art
The filling of the fuel tank of an automobile or other vehicle is commonly accomplished by delivering gasoline through an operator controlled nozzle, and freely pumping the gasoline into the tank. The agitation of the volatile gasoline through the pump and nozzle, and its splashing into the tank of the vehicle, tends to generate a considerable amount of vapor which is ordinarily released to the atmosphere through the fill pipe of the tank. Moreover, as gasoline is dispensed into the fuel tank, it necessarily occupies volume in the tank which had been occupied by air containing a considerable amount of vaporized gasoline. This volume of vapor is necessarily displaced from the tank, generally through the fill pipe into the atmosphere.
The raw gasoline vapor that escapes into the atmosphere during the filling operation presents an economic loss in terms of the actual gasoline lost, and also creates an air pollution problem since the gasoline vapor will react in the atmosphere to produce pollutants. The seriousness of the problem has induced both local and federal governmental agencies to propose regulations as to the amount of gasoline vapor that may be discharged into the atmosphere during the filling operation.
Various devices are available to recapture the gasoline vapor, and either trap it for disposal or recondense the vapor to useable gasoline. The vapor in the fuel tank has typically been collected by such devices through a separate vapor recovery hose, and led back to a storage area where the vapor may be stored, or to a vapor recovery apparatus which extracts liquid gasoline from the vapor. The transport of the gasoline vapor from the fuel tank to the storage or recovery apparatus is typically accomplished either by utilizing an overpressure in the tank provided by sealing the entrance of the tank and discharging fuel thereinto, or by providing a positive vacuum to draw the fuel vapors out of the tank. The first method presents the possibility of overpressurizing and possibly bursting the fuel tank, and the second method may result in an underpressure in the tank, which could draw air into the recovery apparatus and build up an explosive gasoline-air mixture. Apparatus has been developed to control the vacuum present in the vapor recovery line, and thus minimize the possibility of an underpressure in the fuel tank, but such equipment has required the careful monitoring of the pressure and control of the vacuum pump in response to pressure in the vacuum line.